Golf ball material, golf ball, and method for preparing golf ball material

ABSTRACT

The invention provides a golf ball material comprising components (A), (B) and (C): (A) a mixture of different masterbatches prepared by separately masterbatching two or more different metal ions (A1) or a masterbatch prepared by simultaneously masterbatching two or more different metal ions in itself (A2), (B) one or more polymer selected from the group consisting of diene polymers, thermoplastic polymers and thermoset polymers, and (C) one or more polymer having an acid content of from about 0.5 to about 30 wt % and selected from the group consisting of olefin-unsaturated carboxylic acid copolymers, olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester terpolymers, unsaturated carboxylic anhydride-containing polymers, unsaturated dicarboxylic acid-containing polymers and unsaturated dicarboxylic acid half ester-containing polymers. The invention also provides a method for preparing such a golf ball material, and a golf ball made of the material. The golf ball material has a good thermal stability, flow and processability, making it suitable for injection-molding. Moreover, this material is ideal for producing, without any loss of the rebound resilience of golf ball parts molded from the material, high-performance golf balls having excellent durability, scuff resistance and flexibility.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. patent application Ser. No. 11/488,042filed Jul. 18, 2006, now U.S. Pat. No. 7,803,874. The entire disclosureof the prior application is considered part of the disclosure of theaccompanying divisional application, and is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to golf ball materials which have a goodthermal stability, flow and processability and from which there can beobtained high-performance golf balls having excellent properties such asrebound resilience, durability and elasticity. The invention alsorelates to methods for preparing such golf ball materials, and to golfballs which include as a component therein a molded part made from sucha golf ball material.

In recent years, ionomeric resins have been widely used as covermaterials for golf balls. Ionomeric resins are ionic copolymers of anolefin such as ethylene with an unsaturated carboxylic acid such asacrylic acid, methacrylic acid or maleic acid, in which some of the acidgroups are neutralized with metal ions such as sodium, lithium, zinc ormagnesium. These resins provide excellent characteristics in terms ofdurability, rebound resilience and scuff resistance of the ball.

At present, the base resins used in golf ball cover materials aregenerally ionomeric resins, but various improvements are being made tocope with the constant desire by players for golf balls having a highrebound resilience and an excellent flight performance.

For example, to improve the rebound resilience and the costcharacteristics of ionomer cover materials, U.S. Pat. No. 5,312,857,U.S. Pat. No. 5,306,760 and International Application WO 98/46671describe cover materials composed of an ionomeric resin to which a largeamount of a metallic soap has been added.

However, the metallic soap in these cover materials undergodecomposition and vaporization during injection-molding, generating alarge amount of fatty acid gases. As a result, molding defects tend toarise. Moreover, the gases that have formed deposit on the surface ofthe molded part, markedly lowering its paintability. In addition,depending on the type of metallic soap used, significant declines inprocessability and rebound resilience sometimes occur, making the covermaterial entirely unfit for practical use.

In ionomer cover materials, it is a common practice to blend togetherionomers containing different metals so as to improve the reboundresilience and durability (e.g., scuff resistance and low-temperatureimpact resistance), and to use the resulting blend to form golf ballcovers. For example, U.S. Pat. No. 3,819,768 describes the mixture of asodium ionomer of an ethylene-(meth)acrylic acid copolymer with a zincionomer of an ethylene-(meth)acrylic acid copolymer to form a golf ballcover material having rebound resilience improved, and the use of theresulting blend in golf ball covers. However, since this is a two-stepprocess in which, first, ionomers of the different metals are prepared,then the respective ionomers are melt-blended together to give the golfcover material, there have been concerns over deterioration inproperties due to thermal history through the melt-blending andincomplete blending of both ionomers as well as concerns over increasedcosts.

An ionomer that has recently been developed for use as a golf ballmaterial is a homogeneous-phase, high-rebound resilience material havingan interpenetrating polymer network (IPN) structure (U.S. PublishedPatent Application No. 2004/0044136). The ionomer is prepared byblending a first component such as an ethylene-(meth)acrylic acidcopolymer with a different type of thermoplastic resin as a secondcomponent to form a resin composition, then adding as a third componenta metal ionic species to neutralize the acid groups in the firstcomponent dispersed in the resin composition. However, since the resinmaterial prepared by this method contains only one type of metal ion,there is a concern that the physical properties are inferior to those ofresin materials containing a combination of different metal ions.Moreover, since a solid (i.e., a powder or granular material) such as ametal oxide, metal hydroxide or metal carbonate as the metal ionicspecies is used as it is, and also in case of a high acid content in thefirst component, the addition of a large amount of the metal ionicspecies is required for neutralizing the acid groups, during mixing themetal ionic species with the resin components, there are concerns aboutboth poor dispersion of the solid metal ionic species in the resincomponents and leaving some of the metal ionic species unreacted. Inaddition, given that a partial neutralization reaction (incompletedegree of neutralization) occurs and that the target degree ofneutralization cannot be achieved in a one-step reaction throughone-pass extrusion, more than one-pass extrusion be done, which concernsabout lowering the physical properties of the resulting ionomercomposition.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a golf ballmaterial-preparing method in which, in the coexsistence of differentmetal ions, two or more kinds of neutralization reactions of the acidgroups in an acid-containing polymer with different metal ionssimultaneously carry out in a single-step reaction (as a one-passextrusion) to achieve a target degree of neutralization, thereby makingit possible to obtain an ionomeric material containing different metalion crosslinkages (i.e., a mixed metal ionomer). When the ionomericmaterial is used as a golf ball material, it has a good thermalstability, flow and processability without any loss of reboundresilience, from which a high-performance golf ball having excellentdurability and scuff resistance and a suitable hardness can be obtained.A further object of the invention is provide a golf ball which includesas a component therein a molded part made from such a golf ballmaterial.

As a result of extensive investigations, the inventors have discoveredthat by mixing component A with an acid-containing polymer compositionconsisting of component B and component C using a twin-screw reactionextruder;

component A is different metal ionic species such as oxygen-containinginorganic metal compounds, either as (A1) two or more separatelyprepared masterbatches thereof or as (A2) a masterbatch whichsimultaneously contains two or more different metal ionic species initself (A1 and A2 are referred to collectively below as “component A”),

component (B) is one or more polymers selected from the group consistingof diene polymers, thermoplastic polymers and thermoset polymers,

and component (C) is one or more acid-containing polymers having an acidcontent of between 0.5 and 30 wt % and selected from the groupconsisting of olefin-unsaturated carboxylic acid copolymers,olefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterterpolymers, unsaturated carboxylic anhydride-containing polymers,unsaturated dicarboxylic acid-containing polymers and unsaturateddicarboxylic acid half ester-containing polymers;

the neutralization reactions of the acid groups in the acid-containingpolymer composition consisting of components B and C with component Aproceeds smoothly, yielding in a single-step reaction (i.e., in aone-pass extrusion), a material which uniformly contains mixed metal ioncrosslinkages. The inventors have also found that this golf ballmaterial has a surprisingly good thermal stability, flow andprocessability, making it suitable for injection-molding, and that thematerial is ideal for producing, without any loss in the reboundresilience of golf ball parts molded from the material, high-performancegolf balls having excellent durability, scuff resistance andflexibility.

The inventors have also discovered from additional investigations thatgolf balls consisting of a molded part made from such a golf ballmaterial as a ball component (e.g., a cover material in a two-piecesolid golf ball composed of a core and a cover encasing the core, or acover material or intermediate layer material in a multi-piece solidgolf ball composed of a core of at least one layer, at least oneintermediate layer encasing the core and at least one cover layerencasing the intermediate layer) exhibit excellent durability, scuffresistance and elasticity without any loss of rebound.

Accordingly, the invention provides the following golf ball material andmethod for preparing the material and the following golf ball whichincludes as a component therein a molded part made of such a golf ballmaterial.

[I] A golf ball material composed of the following components:

(A) a masterbatch, that is, a concentrate prepared by separatelymasterbatching two or more different metal ions (A1) or a masterbatchprepared by simultaneously masterbatching two or more different metalions (A2);

(B) one or more polymers selected from the group consisting of dienepolymers, thermoplastic polymers and thermoset polymers; and

(C) one or more polymers having an acid content of from about 0.5 toabout 30 wt % and selected from the group consisting ofolefin-unsaturated carboxylic acid copolymers, olefin-unsaturatedcarboxylic acid-unsaturated carboxylic acid ester terpolymers,unsaturated carboxylic anhydride-containing polymers, unsaturateddicarboxylic acid-containing polymers and unsaturated dicarboxylic acidhalf ester-containing polymers.

[II] A method for preparing a golf ball material composed of abovecomponents A, B and C, which includes melt-mixing components B with C toform an acid-containing polymer composition, then melt-mixing componentA with the acid-containing polymer composition to carry out theneutralization reactions of the acid groups in the acid-containingpolymer composition with component A in a single-step reaction (one-passextrusion).

[III] A golf ball which includes a part molded from the above golf ballmaterial, and preferably a golf ball wherein the golf ball material isused as a cover material or an intermediate layer material in atwo-piece solid golf ball having a core and a cover embracing the coreor in a multi-piece solid golf ball having a core of at least one layer,at least one intermediate layer embracing the core, and a cover of atleast one layer embracing the intermediate layer.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described below in more detail.

The golf ball material in the invention consists of the essentialcomponents A, B and C, each of which is described below in detail.

The inventive method for preparing a golf ball material is a methodwherein a material prepared by masterbatching two or more differentmetal ions is used to carry out the neutralization reactions of the acidgroups in an acid-containing polymer composition of components B and C,prepared by melt-blending two or more different types of polymers, in asingle-step reaction (one-pass extrusion), thereby obtaining a materialhaving different metal ion crosslinkages.

That is, the present invention was led as the result of an extensiveinvestigation on (A1) a masterbatch, that is, a concentrate prepared byseparately masterbatching two or more different metal ions or (A2) amasterbatch prepared by simultaneously masterbatching two or moredifferent metal ions, and on extruders for the acid-neutralizingreaction, particularly twin-screw extruders having arranged therein aspecial screw segment, so as to carry out the neutralization reactionsof the acid groups in the acid-containing polymer composition consistedof components B and C in a single-step reaction (one-pass extrusion).

In the invention, to produce a better golf ball material by carrying outthe acid-neutralizing reactions with a combination of different metalions in a single-step reaction (one-pass extrusion) to obtain a targetdegree of neutralization, thereby avoiding thermal history associatedwith both a plurality of extruding passes on the polymer composition toreach a target degree of neutralization and melt-blending differentmetal ion polymers to get a golf ball material, the masterbatch (A),which refers herein to (A1) two or more masterbatches separatelyprepared from two or more different metal ions to be used or (A2) amasterbatch simultaneously prepared from two or more different metalions, is obtained by masterbatching different oxygen-containinginorganic compounds. The different oxygen-containing inorganic metalcompounds used for such masterbatch preparations have an averageparticle size ranging from about 0.005 to about 50 μm, and a particlesize distribution in a range of from about 0.001 to about 300 μm. If theaverage particle size is excessively large, the acid-neutralizingreaction can not proceed to completion. On the other hand, if theaverage particle size is excessively small, its dispersion duringmasterbatch preparation becomes poor. As used herein, “average particlesize” and “particle size distribution” refer to values obtained byparticle size distribution measurement using a laser diffractiontechnique (laser diffraction/scattering).

Two or more different metal ions are used in the invention. Amasterbatch prepared from these metal ions is used as component A. Thatis, component A is either (A1) a material prepared by separatelymasterbatching two or more different metal ions (and composed of two ormore masterbatches), or (A2) a material prepared by simultaneouslymasterbatching two or more different metal ions. By using such amasterbatched material (a masterbatch), the different oxygen-containinginorganic metal compounds which are present therein can be uniformlydispersed during the acid-neutralizing reactions in the acid-containingpolymer composition consisting of components B and C, thus promotingmore uniform reaction with the different metal ions and in turncontributing to uniform properties in the resulting golf ball materialcontaining different metal ion crosslinkages.

When the metal ion sources are not masterbatched, e.g., when two or moredifferent oxygen-containing inorganic metal compounds are mixed directlywith components B and C of the above polymer composition, uniformlydispersing the different oxygen-containing inorganic metal compounds inthe polymer composition is usually difficult. Undispersed and coagulatedpowdery masses typically form, resulting in inhomogeneous reactions,which in turn prevents the desired golf ball material properties frombeing achieved, giving instead a golf ball material that is non-uniformin nature. In particular, if different oxygen-containing inorganic metalcompounds are used in the form of coarse powders, undispersed massesremain in the golf ball material. In such cases, by extruding thepolymer composition several times, the acid-neutralizing reactions canbe completed to the target degree of neutralization. To illustrate, U.S.Published Patent Application No. 2004/0044136 describes an example inwhich magnesium hydroxide alone is used as the metal ionic species andthe acid-containing polymer is passed several times through a twin-screwextruder to promote the neutralization reaction.

The above different metal ions, while not subject to any particularlimitation, are typically a combination of a monovalent metal ion with adivalent metal ion, preferred examples of which include Na/Mg, Li/Mg,Na/Zn, Na/Ca and Na/Zn/Ca. The relative proportions of the differentmetal ions are preferably such that the weight ratio of monovalent metalions to divalent metal ions is from about 2/98 to about 98/2.

In the practice of the invention, the different oxygen-containinginorganic compounds used in (A1) a material prepared by separatelymasterbatching two or more different metal ions or (A2) a materialprepared by simultaneously masterbatching two or more different metalions are metal oxides, metal carbonates or metal hydroxides, and themetal ionic species are selected from among groups IA, IB, IIA, IIB,IIIA, IIIB, IVA, IVB, VA, VB, VIIA, VIIB, VIIB and VIIIB of the periodictable. Illustrative, non-limiting, examples of the differentoxygen-containing inorganic compounds include lithium carbonate, sodiumcarbonate, potassium carbonate, magnesium carbonate, zinc carbonate,magnesium hydroxide, magnesium oxide, calcium hydroxide, calcium oxideand zinc oxide. Two or more different compounds are used.

The above oxygen-containing inorganic metal compounds have an averageparticle size which, while not subject to any particular limitation, ispreferably from about 0.005 to about 50 μm, and more preferably fromabout 0.010 to about 20 μm. The particle size distribution, while notsubject to any particular limitation, is preferably from about 0.001 toabout 300 μm, and more preferably from about 0.005 to about 100 μm.

Also, by preferentially masterbatching different organic acid-freeoxygen-containing inorganic metal compounds which do not release organicacids following the acid-neutralizing reactions, it is possible topromote uniform reactions and to suppress corrosive effects on themanufacturing equipment. Hence, the use of such an approach ispreferred.

In such a case, it is advantageous for the base polymer used in themasterbatch of component A to be one having a high melt flow rate (MFR).Specifically, the base polymer is typically one having a melt flow rateof preferably at least about 10 g/10 min, more preferably at least about50 g/10 min, and even more preferably at least about 100 g/10 min. Usecan also be made of a liquid wax such as a high-MFR ethylene wax, or alow-acid, high-MFR ethylene polymer. Illustrative examples includePolyethylene Wax AC5120 (available from Tomen Plastics Corporation;acrylic acid content, 15 wt %; MFR, >1,000 g/10 min), Nucrel 599(available from DuPont; methacrylic acid content, 10 wt %; MFR, 450 g/10min), Nucrel 699 (available from DuPont; methacrylic acid content, 11 wt%; MFR, 100 g/10 min), and Nucrel N0200H (available from DuPont;methacrylic acid content, 2 wt %; MFR, 130 g/10 min).

The concentration of the above different oxygen-containing inorganicmetal compounds is typically from about 10 to about 90 wt %, preferablyfrom about 20 to about 80 wt %, and more preferably from about 30 toabout 70 wt %. If the concentration of the different oxygen-containinginorganic metal compounds in the masterbatch is excessively high, themasterbatch becomes an unacceptably low melt flow rate (MFR) of below0.1 W10 min. In such a case, when the masterbatch is blended togetherwith the above-described acid-containing polymer composition (componentsB and C), the different oxygen-containing inorganic metal compounds inthe masterbatch can not disperse well. On the other hand, if theconcentration is too low, a larger amount of the masterbatch is added,as a result of which the high-MFR thermoplastic resin (particularlyethylene waxes and low-acid, high-MFR ethylene polymers) used in themasterbatch causes a detrimental effect on the physical properties ofthe golf ball material.

The amount of component A included in the golf ball material isdetermined by the target degree of neutralization of the acid groupspresent in the acid-containing polymer composition (components B and C).Excess component A results in a high degree of neutralization, loweringthe melt flow rate (MFR) of the golf ball material and thus adverselyaffecting the processability. On the other hand, the excessively smalldiminishes the physical properties of the golf ball material and resultin a poor rebound resilience and a poor durability in golf ballsobtained therefrom.

The method for preparing masterbatches as component A involves the useof an apparatus selected from among twin-screw/single-screw extruders(including kneader-extruders) equipped with a kneader such as apressurizing kneader and a force feeder, tandem extruders (consisting ofa twin-screw extruder for upstream processing and a vacuum-ventedextruder for downstream processing), and vacuum-vented twin-screwextruders. It is preferable either to use a twin-screw/single-screwextruder equipped with a kneader and a force feeder or to use a tandemextruder. Using these extruders, the different oxygen-containinginorganic compounds and the base polymer are dry-blended before feedingor are feeded each into the hopper from separate feeders. The mixingtemperature is adjusted within a range of about 50 to about 250° C., andpreferably about 80 to about 230° C.

The acid-neutralizing reactions of above component A with theacid-containing polymer composition (components B and C) can be effectedby mixing the various above components using, for example, an internalmixer such as a twin-screw extruder, a Banbury mixer, a kneader or aLabo Plastomill. The extruder used for preparing the golf ball materialis preferably a twin-screw extruder. A twin-screw extruder havingfeatures (i) to (v) below is especially preferred.

(i) An effective screw length L/D (i.e., screw length-to-diameter ratio)of 20 or more, preferably 25 or more, and more preferably 30 or more.

(ii) A screw segment configuration in which the L/D ratio of thekneading disc zone is about from 10 to about 90%, preferably from about20 to about 80%, and more preferably from about 30 to about 70%, of theoverall L/D.

Also, the discs in the kneading disc zone of the twin-screw extruderinclude right-handed kneading discs, left-handed kneading discs, reversediscs, and various neutral discs.

(iii) A screw diameter of 15 mm or more.

(iv) A vent port and a vacuum line connected thereto.

(v) A device for the dropwise addition or pressurized injection of aliquid.

In the single-step acid-neutralizing reaction carried out in the methodof the invention with the masterbatch A (component A) of two or moredifferent metal ions (component A), above components B and C aremelt-blended to form a molten polymer composition of components B and C.Above component A is then melt-blended into the molten polymercomposition, and a liquid may be added (by injection under pressure ordropwise addition) to promote the neutralization reaction in which atleast some of the acid groups present in the polymer composition(components B and C) are neutralized. The liquid in this case ispreferably a compound shown by the formula ROH, where R represents ahydrogen or an alkyl group. The amount in weight percent of the liquidadded versus the resin output (kg) per hour, based on the overall resinextrusion rate, is preferably from about 0.1 to about 10 wt %, morepreferably from about 0.5 to about 8 wt %, and even more preferably fromabout 1.0 to about 5.0 wt %.

The heating conditions (barrel-setting temperatures) can be set to, forexample, from 100 to 250° C., although melt-mixing is preferably carriedout at a temperature which exceeds both the melting point of component Band the melting point of component C.

Although the mixing method is not subject to any particular limitation,for better microdispersion of component B it is preferable to firstthoroughly melt-mix components B and C so as to form the polymercomposition of components B and C, then to add and incorporate componentA (i.e., component A1 and/or component A2). If additives are to beincluded, the additives are able to be added and blended into thecomposition following the incorporation of component A.

In the practice of the invention, the acid-neutralizing reactions of theacid-containing polymer composition (components B and C) with themasterbatched material of two or more different metal ions (component A)is carried out in a single-step reaction. The acid-neutralizing reactionin the twin-screw reaction extruder used for this purpose is carried outat a temperature ranging of from about 110 to about 260° C., preferablyfrom about 130 to about 240° C., and more preferably from about 170 toabout 230° C. The extrusion rate (the output) for a screw diameter D of32 mm is from about 2 to about 60 kg/h, preferably from about 4 to about40 kg/h, and more preferably from about 5 to about 30 kg/h. Moreover, ifthe screw diameter ratio D₁/D₂ (D₁ being larger than D₂) is A, theextrusion rate (the output) on scale-up of the twin-screw extruder isproportional to A^(1.0) to A^(3.0) within a range of preferably fromA^(1.0) to A^(3.0), and more preferably in an exponential range of from1.5 to 2.7; i.e., from A^(1.5) to A^(2.7.)

It is preferable for the golf ball material of the invention to have amelt flow rate (MFR) within a specific range so as to ensure that it hasflow properties well-suited for injection molding and to improve itsprocessability. The melt flow rate is generally at least about 0.1 g/10min, and preferably at least about 0.5 g/10 min, but generally not morethan about 50 g/10 min, and preferably not more than about 30 g/10 min.A melt flow rate which is excessively high or excessively lowsignificantly lowers the processability. As used herein, “melt flowrate” refers to a measured value obtained according to JIS-K7210 at atesting temperature of 190° C. and under a testing load of 21.18 N (2.16kgf).

The golf ball material of the invention has, in Fourier transforminfrared absorption spectroscopic (FT-IR) measurements, an absorptionpeak attributable to carbonyl stretching vibrations at 1690 to 1710 cm⁻¹and an absorption peak attributable to the carboxylate anion stretchingvibrations of a metal carboxylate at 1530 to 1630 cm⁻¹, confirming thatthe acid-neutralizing reactions has taken place and confirming thepresence of metal ionic crosslinks.

Molded parts obtained using the golf ball material of the invention havea Shore D hardness of generally at least about 50, and preferably atleast about 52, but generally not more than about 75, and preferably notmore than about 70. If the molded part has an excessively high Shore Dhardness, the “soft feeling” of the ball when hit diminishessignificantly. On the other hand, if the Shore D hardness is excessivelylow, the rebound of the ball decreases.

Component B in the invention is one or more polymers selected from thegroup consisting of diene polymers, thermoplastic polymers and thermosetpolymers. Illustrative examples include polymers and polymercompositions composed of one or more selected from the group consistingof polyolefin elastomers, polystyrene elastomers, polyacrylate polymers,polyamide elastomers, polyurethane elastomers, polyester elastomers,diene polymers, polyacetals (POM), epoxy resins, unsaturated polyesterresins, silicone resins and ABS resins.

In the golf ball material of the invention, when component B is athermoplastic polymer, the acid-containing polymer composition ofcomponents B and C has a weight ratio of component B to component C(B/C) of from about 99/1 to about 1/99.

When component B is a thermoset polymer, the weight ratio of component Bto component C (B/C) in the acid-containing polymer composition ofcomponents B and C is from about 49/51 to about 1/99.

Component C in the inventive golf ball material is a polymer compositionwhich has an acid content of from about 0.5 to about 30 wt %, andpreferably from about 1.0 to about 25 wt %, and is one or more selectedfrom the group consisting of olefin-unsaturated carboxylic acidcopolymers, olefin-unsaturated carboxylic acid-unsaturated carboxylicacid ester terpolymers, unsaturated carboxylic anhydride-containingpolymers, unsaturated dicarboxylic acid-containing polymers andunsaturated dicarboxylic acid half ester-containing polymers.

When component C is an olefin-unsaturated carboxylic acid copolymer, theolefin is generally one having at least 2 carbons, but not more than 8carbons, and especially not more than 6 carbons. Illustrative examplesof such olefins include ethylene, propylene, butene, pentene, hexene,heptene and octene. Ethylene is especially preferred. Illustrativeexamples of the unsaturated carboxylic acid include acrylic acid,methacrylic acid, maleic acid, maleic anhydride, and fumaric acid.Acrylic acid and methacrylic acid are especially preferred.

When component C is an olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester terpolymer, the olefin and the unsaturatedcarboxylic acid are exemplified by the same olefins and unsaturatedcarboxylic acids as in the above-described olefin-unsaturated carboxylicacid copolymer. The unsaturated carboxylic acid ester is preferably alower alkyl ester of the above unsaturated carboxylic acids,illustrative examples of which include methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, methyl acrylate,ethyl acrylate, propyl acrylate and butyl acrylate. The use of butylacrylate (n-butyl acrylate, isobutyl acrylate) is especially preferred.

When component C is selected from among unsaturated carboxylicanhydride-containing polymers, unsaturated dicarboxylic acid-containingpolymers and unsaturated dicarboxylic acid half ester-containingpolymers, a polymer composed of an olefin and at least one compoundselected from among unsaturated carboxylic anhydrides, unsaturateddicarboxylic acids and unsaturated dicarboxylic acid half esters ispreferred. Examples of unsaturated carboxylic anhydrides include maleicanhydride and itaconic anhydride, with maleic anhydride being especiallypreferred. Examples of unsaturated dicarboxylic acids include maleicacid, fumaric acid and itaconic acid. Examples of unsaturateddicarboxylic acid half esters include monoesters of the foregoingdicarboxylic acids, such as the monoethyl ester of maleic acid, themonomethyl ester of fumaric acid and the monoethyl ester of itaconicacid. The monoethyl ester of maleic acid is especially preferred. Theolefin is preferably one having generally at least two carbons, but notmore than 8 carbons, and especially not more than 6 carbons. Examples ofsuch olefins include ethylene, propylene, butene, pentene, hexene,heptene and octene. Of these, the use of ethylene is especiallypreferred.

The unsaturated carboxylic anhydride-containing polymer, unsaturateddicarboxylic acid-containing polymer and unsaturated dicarboxylic acidhalf ester-containing polymer in above component C are exemplified by,but not limited to, the following polymers:

(i) olefin polymers to which has been grafted an unsaturated carboxylicanhydride, an unsaturated dicarboxylic acid and/or an unsaturatedcarboxylic acid;

(ii) olefin-unsaturated carboxylic acid polymers to which has beengrafted an unsaturated carboxylic anhydride, an unsaturated dicarboxylicacid and/or an unsaturated carboxylic acid;

(iii) olefin-unsaturated carboxylic acid ester polymers to which hasbeen grafted an unsaturated carboxylic anhydride, an unsaturateddicarboxylic acid and/or an unsaturated carboxylic acid;

(iv) olefin-unsaturated carboxylic acid-unsaturated carboxylic acidester polymers to which has been grafted an unsaturated carboxylicanhydride, an unsaturated dicarboxylic acid and/or an unsaturatedcarboxylic acid;

(v) olefin-unsaturated carboxylic anhydride-unsaturated carboxylic acidester polymers;

(vi) olefin-unsaturated dicarboxylic acid-unsaturated carboxylic acidester polymers; and

(vii) olefin-unsaturated dicarboxylic acid half ester-unsaturatedcarboxylic acid ester polymers.

Each of the above copolymers can be obtained using a known method forcopolymerization and grafting. If the acid content within the copolymeris excessively low, the rebound resilience and the strength (tensilestrength at break) decrease. If it is excessively high, theprocessability decreases.

Examples of commercial products that are used as component C includeolefin-unsaturated carboxylic acid polymers such as Nucrel 960 andNucrel 2806 (both products of DuPont), and ESCOR5200, ESCOR5100 andESCOR5000 (all products of Exxon-Mobil Chemical).

Examples of olefin-unsaturated carboxylic acid-unsaturated carboxylicacid ester polymers include Bynel 2002, Bynel 2014, Bynel 2022 and BynelE403 (all products of DuPont), and ESCOR ATX325, ESCOR ATX320 and ESCORATX310 (all products of Exxon-Mobil Chemical).

Examples of unsaturated carboxylic anhydride polymers include MODIPERA8100, MODIPER A8200 and MODIPER A8400 (all products of NORCorporation), and LOTADER 3200, LOTADER 3300, LOTADER 5500, LOTADER6200, LOTADER 7500, LOTADER 8200, LOTADER TX8030 and LOTADER TX8390 (allproducts of ATOFINA and ARKEMA).

Examples of commercial unsaturated carboxylic anhydride-grafted polymersinclude Polybond 3009, Polybond 3200 and Royaltough 498 (all products ofUniroyal Chemical), ADOMER NF518 and ADOMER QE800 (both products ofMitsui Chemicals, Inc.), Bynel 2167, Bynel 2174, Bynel 4206, Bynel 4288,Bynel 50E561 and Bynel 50E571 (all products of DuPont), and ExxelorVA1801, Exxelor VA1803, Exxelor VA 1840 and Exxelor PO1020 (all productsof Exxon-Mobil Chemical).

In the golf ball material of the invention, by also including anorbornene dicarboxylic anhydride and/or a derivative thereof and aperoxide, together with the above-described essential components A, Band C, followed by carrying out the acid neutralizing reactions togetherwith the grafting reaction of the norbornene dicarboxylic anhydrideand/or a derivative thereof onto components B with C, there can beobtained a resin composition having an interpenetrating network (IPN)structure which suppresses delamination by component B. The norbornenedicarboxylic anhydride and/or derivative thereof are exemplified asfollows.

Norbornene ring derivatives include halogen-, alkyl-, aryl- andaralkylnorbornenes; and dicarboxylic anhydride derivatives includedicarboxylic acids, dicarboximides and derivatives thereof.Stereoisomers of dicarboxylic anhydrides and their derivatives to thenorbornene ring includes the exo isomers, endo isomers and mixturesthereof. Illustrative examples includecis-5-norbornene-endo-2,3-dicarboxylic anhydride,cis-5-norbornene-exo-2,3-dicarboxylic anhydride,methyl-cis-5-norbornene-endo-2,3-dicarboxylic anhydride,cis-5-norbornene-endo-2,3-dicarboximide and1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic anhydride. Thesecompounds are included in an amount, per 100 parts by weight of abovecomponents B and C combined, of generally about 0.05 to about 20 partsby weight, preferably about 0.1 to about 10 parts by weight, and morepreferably about 0.2 to about 5.0 parts by weight. If these compoundsare added in excess, the resulting resin composition exhibits a drasticdecline in melt flow rate (MFR) and causes gel formation, which makes itimpossible to obtain normal molded parts. Conversely, if these compoundsare added in an excessively small amount, the resulting resincomposition causes delamination arisen during injection molding,possibly resulting in a poor scuff resistance and a low rebound, andthus having an adverse influence on the properties of the golf ballobtained as the finished product.

When a norbornene dicarboxylic anhydride and/or a derivative thereof isalso included in the golf ball material of the invention, duringpreparation of the resin composition containing above components A, Band C, a resin composition having an IPN structure can be obtained bymelt-mixing components B and C together with the norbornene dicarboxylicanhydride and/or a derivative thereof and a peroxide at a lowtemperature at which the peroxide does not decompose prematurely, thenadding the metal ionic species (e.g., oxygen-containing inorganic metalcompounds) of component A and melt-mixing at or above the temperature atwhich the peroxide decomposes so as to effect both the grafting of thenorbornene dicarboxylic anhydride and/or a derivative thereof and theacid-neutralizing reaction. It is preferable here to follow a procedurein which first the norbornene dicarboxylic anhydride and/or a derivativethereof, the peroxide and component B are melt-mixed at a temperaturelow enough so that the peroxide does not decompose prematurely, then theacid-containing polymer used as component C is melt-mixed at atemperature low enough so that the peroxide does not decompose,following which the metal ionic species (e.g., oxygen-containinginorganic metal compounds) of component A is added and melt-mixing iscarried out at or above the temperature at which the peroxide decomposesso as to carry out both the grafting of the norbornene dicarboxylicanhydride and/or a derivative thereof and the acid-neutralizingreaction.

The peroxide used together with the norbornene dicarboxylic anhydrideand/or a derivative thereof are selected appropriately based on thedecomposition temperature thereof and the melting temperature at whichcomponent B and/or component C can be kneaded. The peroxide typicallyhas a 1-minute half-life temperature of from about 140° C. to about 250°C., preferably about 150° C. to about 230° C., and more preferably about160° C. to about 210° C. Illustrative examples of such peroxides thatare utilized include one or more selected from among dicumyl peroxide(1-minute half-life temperature, 175° C.), di-t-butyl peroxide (185°C.), 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne (194° C.),n-butyl-4,4-di(t-butylperoxy)valerate (173° C.),di(2-t-butylperoxyisopropyl)benzene (175° C.), di-t-hexyl peroxide (177°C.) and p-menthanehydroperoxide (200° C.). Of these, the use of dicumylperoxide, di-t-butyl peroxide and2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne is preferred. It isdesirable to set the amount of the peroxide included, based on thecombined amount of components B and C, at preferably from about 0.01 toabout 20 parts by weight, more preferably from about 0.05 to about 15parts by weight, even more preferably from about 0.09 to about 10 partsby weight, and most preferably from about 0.1 to about 5.0 parts byweight.

The golf ball material of the invention may additionally includeoptional additives appropriately for the intended use. When theinventive golf ball material is used as a cover material, variousadditives such as pigments, dispersants, compatibilizing agents,antioxidants, ultraviolet absorbers and crosslinking agents are added toabove components A to C. For example, a norbornene carboxylic anhydrideor a derivative thereof may be included as a compatibilizing agent and aperoxide may be included as a crosslinking agent. When such additivesare included, they are added in an amount of generally at least about0.1 part by weight, and preferably at least about 0.5 part by weight,but generally not more than about 20 parts by weight, and preferably notmore than about 15 parts by weight, per 100 parts by weight of abovecomponents A to C combined.

The golf ball material of the invention has a specific gravity ofgenerally at least about 0.9, preferably at least about 0.92, and morepreferably at least about 0.94, but generally not more than about 1.3,preferably not more than about 1.2, and more preferably not more thanabout 1.05.

The golf ball of the invention includes as an essential ball component apart molded from the above-described golf ball material of theinvention. Parts molded from the inventive golf ball material are usedas either a portion of the golf ball or the entire golf ball. Examplesinclude the cover of a thread-wound golf ball in which the cover has asingle-layer structure or a multilayer structure of two or more layers;a one-piece golf ball; the solid core or the cover of a two-piece solidgolf ball; and the solid core, the intermediate layer or the cover of amulti-piece solid golf ball such as a three-piece solid golf ball. Theinventive golf ball is not subject to any particular limitation, insofaras it is a golf ball that includes as a ball component therein a partmolded from the golf ball material of the invention.

It is particularly advantageous for the golf ball material of theinvention to be used as the cover material in a two-piece solid golfball composed of a core and a cover embracing the core, or as the covermaterial or the intermediate layer material in a multi-piece solid golfball composed of a core of at least one layer, at least one intermediatelayer embracing the core, and a cover of at least one layer encasing theintermediate layer.

Two-piece solid golf balls composed of a polybutadiene (BR) core and acover injection-molded from a golf ball material prepared by theabove-described method of the invention were manufactured and tested,from which it was found that golf balls having the performances andqualities indicated below can be obtained. Here, golf balls made usingcover materials obtained by simultaneous acid-neutralizing reactionsinvolving an oxygen-containing inorganic metal compound masterbatch (A)(examples according to the invention) were compared with golf balls madeusing, as controls, cover materials obtained from a correspondingmelt-blend (comparative examples).

-   a) Excellently uniform cover's surface.-   b) Excellent scuff resistance.-   c) Excellent durability (number of shots).-   d) High flow properties (MFR).-   e) High rebound resilience.-   f) Interpenetrating polymer network structure aside from sea-island    (salt and pepper) structure.

In the inventive golf ball material and the inventive method ofpreparation, therefore, by carrying to completion in a single-stepreaction (one-pass extrusion) simultaneous neutralization reactions ofthe acid groups in an acid-containing polymer with a mixture ofdifferent masterbatches having a different metal ion source each or amasterbatch having different metal ion sources in itself, is a materialcontaining different metal ion crosslinkages obtained without mixing twoor more ionomer materials which are produced respectively to obtain amaterial as nearly same as the inventive material in an aftertreatment,and has a good thermal stability, flow and processability without anyloss of rebound resilience, enabling high-performance golf ballmaterials of excellent durability, scuff resistance and elasticity to beobtained.

EXAMPLES

Reference Examples and Examples of the invention are given below by wayof illustration and not by way of limitation. The twin-screw reactionextruder used in the examples of the invention for the acid-neutralizingreactions had a screw diameter of 32 mm, an overall L/D ratio of 41, anL/D ratio in the kneading disc zone which was 40% of the overall L/Dratio, and was equipped with a vacuum-venting port and a pressuredwater-injecting device.

Reference Example 1 Preparation of a Magnesium Hydroxide Masterbatch

A 5-liter pressurizing kneader (manufactured by Naniwa MachineryManufacturing Co., Ltd.; setting temperature, 100° C.) was used toprepare a masterbatch (MB) from an ethylene-methacrylic acid-acrylicacid ester terpolymer (available from DuPont; MFR, 130 g/10 min) as thebase polymer and magnesium hydroxide Mg(OH)₂ (Kyowa Chemical IndustryCo., Ltd.; average particle size, 0.6 μm). The kneader was charged witha combined amount of 2.5 kg of the base polymer and the magnesiumhydroxide in a 50/50 weight ratio, and mixing was carried out for 20minutes under an applied pressure of 0.49 MPa at a rotor speed of 20 rpmand at a mixing temperature controlled to not above 105° C. The mixturewas discharged as a strand from a 40 mm-in-diametertwin-screw/single-screw extruder (Naniwa Machinery Manufacturing Co.,Ltd.; setting temperature, 170° C.), then passed through a cooling waterbath, an air knife, and a pelletizer. The melt flow rate of theresulting magnesium hydroxide masterbatch having a magnesium hydroxidecontent of 50 wt % was 1.9 g/10 min (measured at 190° C. under a load of2,160 g). This magnesium hydroxide masterbatch is abbreviated below as“MgMB.”

Reference Example 2 Preparation of a Sodium Carbonate Masterbatch

Aside from using sodium carbonate Na₂CO₃ (available from TokuyamaCorporation; average particle size of ground material, 5 μn) instead ofmagnesium hydroxide, the same procedure was done as in Reference Example1 using the same mixing ratio, i.e., a 50/50 weight ratio between thebase polymer and the sodium carbonate. The resulting sodium carbonatemasterbatch with a sodium carbonate content of 50 wt % had a melt flowrate of 2.5 g/10 min (at 190° C. under a 2,160 g load). This sodiumcarbonate master batch is abbreviated below as “NaMB.”

Reference Example 3 Preparation of a Mixed Masterbatch

Aside from setting the proportions in which magnesium hydroxide Mg(OH)₂and sodium carbonate Na₂CO₃ are mixed to 1.30/3.70 so as to provide thespecific degrees of neutralization (mol %) by the respective metal ionsshown in Table 1 and using the corresponding amounts of both compounds,the same procedure was conducted as in Reference Example 1. Theresulting mixed masterbatch containing 50 wt % of magnesium hydroxideand sodium carbonate had a melt flow rate of 3 g/10 min (measured at190° C. under a 2,160 g load). This mixed master batch is abbreviatedbelow as “MgNaMB.”

Example 1

Using the thermoplastic polyurethane elastomer (TPU) (produced by DICBayer Polymer, Ltd. under the trade name Pandex; Shore A hardness, 85)as component B in the invention, and using the ethylene-methacrylic acidcopolymer (Polymer 1) (DuPont; MFR, 60 g/10 min), theethylene-methacrylic acid copolymer (Polymer 2)(DuPont; MFR, 500 g/10min) and the ethylene-methacrylic acid-isobutyl acrylate terpolymer(Polymer 3) (DuPont; MFR, 31 g/10 min) as component C, melt-mixing wascarried out in the proportions shown in Table 1 within a twin-screwreaction extruder set at 160° C. The mixture was extruded as a strandfrom the extruder die, and passed through a cooling water bath. Excesswater was removed with an air knife, then the strand was cut intopellets with a pelletizer, giving a uniform mixed composition ofTPU/Polymer 1/Polymer 2/Polymer 3.

Next, pellets of the resulting TPU/Polymer 1/Polymer 2/Polymer 3 mixturewere dry-blended in the proportions shown in Table 1 with the NaMBprepared in Reference Example 2 and the MgMB prepared in ReferenceExample 1. The blend was then fed to the hopper of a twin-screw reactionextruder set at 195° C., and subjected to an acid-neutralizing reactions(to respective levels of neutrality of 40%) at the screw speed of 120rpm and the extrusion rate (output) of 5.5 kg/hr while injecting waterpressured with a liquid injection pump attached to the twin-screwreaction extruder in the amount of 3 wt % with respect to the resinoutput and while removing volatiles through the vacuum vent. The stranddischarged from the extruder die was passed through a cooling waterbath, excess water was removed with an air knife, and the strand was cutinto pellets with a pelletizer, giving the uniform TPU-containingNa/Mg-ionomer composition. Pellets of the resulting uniform, transparentmixed composition were used to form a 3 mm thick sheet having a lengthand width of 150 mm each in a hot press compression molding machine. Thesheet was visually observed, and found to be free of NaMB and MgMB inunreacted form or as powdery masses.

In addition, titanium dioxide and a blue pigment were dry-blended withthis uniform TPU-containing Na/Mg-ionomer composition in the proportionsshown in Table 1, then melt-mixed in a twin-screw reaction extruder setat 195° C. at the screw speed of 100 rpm and the extrusion rate (output)of 8.5 kg/hr while using a vacuum vent. The strand discharged from theextruder die was passed through a cooling water bath, following whichexcess water was removed with an air knife, and the strand was cut intopellets with a pelletizer, yielding the TPU-containing Na/Mg-ionomergolf ball material (TPU-NaMg Ionomer 1). The properties of this golfball material were evaluated. As shown in Table 1, the golf ballmaterial had a suitable hardness and exhibited a melt flow rate whichindicated that it was injection-moldable.

The above golf ball material was employed as the cover material for atwo-piece golf ball by being injection-molded over a core of crosslinkedpolybutadiene (core diameter, 38.9; weight, 36.0 g; compressive straindeflection, 3.35 mm) using an injection molding machine (settingtemperatures: hopper, 160° C.; C1 to die head, 180 to 210° C.) at theinjection pressure of 5.9 MPa, the holding pressure of 4.9 MPa, theinjection and holding time of 8 seconds, and the cooling time of 25seconds, thereby producing two-piece golf balls. After injectionmolding, the surface of the golf ball was trimmed, yielding the finishedgolf balls (diameter, 42.7 mm; weight, 45.5 g) having a smooth surfacefree of burrs. These golf balls were then evaluated. The results areshown in Table 1, indicating that the golf balls had a good scuffresistance, a good ball durability (see Comparative Examples 1 and 2), ahigh initial velocity and a high coefficient of restitution (COR). Theball properties were comparable with those obtained in ComparativeExample 5 using a corresponding melt-blend, thus confirming theadvantageous effects provided by the simultaneous presence of differentmetal ions.

Example 2

Aside from adding the norbornene dicarboxylic anhydride (α-1) (availablefrom Hitachi Chemical Co., Ltd.; 5-norbornene-2,3-dicarboxylicanhydride) as both the low-molecular-weight compatibilizing agent andthe crosslinking agent, and the peroxide (PO) (available from NORCorporation); 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 in theproportions indicated in Table 1, the same procedure was carried out asin Example 1, giving the uniform TPU-containing Na/Mg-ionomer golf ballmaterial (TPU-NaMg Ionomer 2). This golf ball material and the golfballs made with the material were evaluated. The results are shown inTable 1. The ball properties were comparable with the results obtainedin Comparative Example 6 using a corresponding melt blend, thusconfirming the advantageous effects provided by the simultaneouspresence of different metal ions.

Example 3

Aside from using the ethylene-ethyl acrylate-maleic anhydride terpolymerPolymer 4 (available from ARKEMA; MFR, 7 g/10 min) instead of Polymer 3in the proportions indicated in Table 1, the same procedure was carriedout as in Example 2, giving the uniform TPU-containing Na/Mg-ionomergolf ball material (TPU-NaMg Ionomer 3). This golf ball material and thegolf balls made with the material were evaluated. The results are shownin Table 1. The ball properties were comparable with the resultsobtained in Comparative Example 7 using the corresponding melt-blend,thus confirming the advantageous effects provided by the simultaneouspresence of different metal ions.

Example 4

Aside from using the Na.MgMB prepared in Reference Example 3 in theproportions indicated in Table 1 instead of NaMB and MgMB, the sameprocedure was carried out as in Example 3, giving the uniformTPU-containing Na/Mg-ionomer golf ball material (TPU-NaMg Ionomer 4).This golf ball material and the golf balls made with the material wereevaluated. The results are shown in Table 1. Excellent propertiescomparable with those in Example 3 were obtained.

Comparative Example 1

The NaMB prepared in Reference Example 2 was used in the mixingproportions indicated in Table 1 to subject Polymer 1 to theacid-neutralizing reactions carried out in Example 1 with the twin-screwreaction extruder, thereby preparing the Na-ionomer component (40 mol %Na-Polymer 1) neutralized to the same degree as the TPU-NaMg Ionomer 1prepared in Example 1, and the Na Ionomer 1 melt-mixed with titaniumoxide and blue pigment was obtained. The resulting golf ball materialand the golf balls made with the material were evaluated. The resultsare shown in Table 1.

With the sodium ionic species alone, the durability and scuff resistanceof the golf balls were inferior to those obtained in Example 1 using thecombination of different metal ions.

Comparative Example 2

The MgMB prepared in Reference Example 1 was used in the mixingproportions indicated in Table 1 to prepare the TPU-containingMg-ionomer composition (40 mol % Mg-Polymer 1/Polymer 2/Polymer 3)neutralized to the same degree as the TPU-NaMg Ionomer 1 compositionprepared in Example 1, according to the method described in Example 1.The Mg-ionomer composition was assigned as TPU Mg Ionomer 1. Theresulting golf ball material and the golf balls made with the materialwere evaluated. The results are shown in Table 1. With the magnesiumionic species alone, the golf balls had a durability far inferior tothat of the golf balls obtained in Example 1.

Comparative Example 3

The TPU, α-1 and the peroxide-containing Mg-ionomer composition (40 mol% Mg-Polymer 1/Polymer 2/Polymer 3) was obtained as TPU-Mg Ionomer 2 bymelt-mixing those ingredients in the proportions indicated in Table 1,followed by neutralizing them with the MgMB to the same degree asTPU-NaMg Ionomer 2 composition prepared in Example 2, according to themethod described in Example 2. The resulting golf ball material and thegolf balls made with the material were evaluated. The results are shownin Table 1. This was the material prepared for melt-blending inComparative Example 6 serving as the control for Example 2 of theinvention. Due to the incorporation of the crosslinkable compatibilizingagent α-1 and the peroxide, the golf ball properties were better than inComparative Example 2.

Comparative Example 4

The TPU, α-1 and the peroxide-containing Mg-ionomer composition (40 mol% Mg-Polymer 1/Polymer 2/Polymer 3), assigned as TPU-Mg Ionomer 3, wasprepared by melt-mixing those ingredients in the proportions indicatedin Table 1, followed by neutralizing them with the MgMB according to themethod described in Example 3. The resulting golf ball material and thegolf balls made of the material were evaluated. The results are shown inTable 1. This was the material prepared for melt-blending in ComparativeExample 7 serving as the control for Examples 3 and 4 of the invention.Due to the incorporation of the soft component Polymer 4, the golf ballhad a somewhat rough surface after being trimmed.

Comparative Example 5 Control for Example 1

The Na Ionomer 1 prepared in Comparative Example 1 and the TPU-MgIonomer 1 prepared in Comparative Example 2 were dry-blended in theproportions indicated in Table 1. Using the same twin-screw reactionextruder as in Example 1, the dry blend was then melt-blended withoutwater injection, at 195° C., with vacuum venting, at the screw speed of100 rpm and at the extrusion rate (output) of 8.5 kg/hr to give TPU-NaMgBlend 1. The resulting golf ball material and the golf balls made withthe material were evaluated. The results are shown in Table 1. Due tothe effect of melt-blending different metal ions, a particularimprovement in durability over the results obtained in ComparativeExamples 1 and 2 was observed.

Comparative Example 6 Control for Example 2

The Na Ionomer 1 prepared in Comparative Example 1 and the TPU-MgIonomer 2 prepared in Comparative Example 3 were dry-blended in theproportions indicated in Table 1. The same procedure was followed as inComparative Example 5 using the same twin-screw reaction extruder as inExample 1, thereby giving TPU-NaMg Blend 2. The resulting golf ballmaterial and the golf balls made with the material were evaluated. Theresults are shown in Table 1.

Comparative Example 7 Control for Example 3

The Na Ionomer 1 prepared in Comparative Example 1 and the TPU-MgIonomer 3 prepared in Comparative Example 4 were dry-blended in theproportions indicated in Table 1. The same procedure was followed as inComparative Example 5 using the same twin-screw reaction extruder as inExample 1, thereby giving TPU-NaMg Blend 3. The resulting golf ballmaterial and the golf balls made with the material were evaluated. Theresults are shown in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Example 4 TPU-NaMg TPU-NaMgTPU-NaMg TPU-NaMg Ionomer 1 Ionomer 2 Ionomer 3 Ionomer 4 a. Na•MgMB — —— 9.98 b. NaMB 7.40 7.40 7.40 — c. MgMB 2.91 2.91 2.58 — d. TPU 20.020.0 20.0 20.0 e. a-1 — 0.7 0.7 0.7 f. PO — 0.23 0.2 0.2 g. Polymer 159.2 59.2 56.8 56.8 h. Polymer 2 10.0 10.0 10.0 10.0 i. Polymer 3 10.810.8 — — j. Polymer 4 — — 13.2 13.2 k. TiO₂ 2.0 2.0 2.0 2.0 l. Bluepigment 0.04 0.04 0.03 0.03 g′. Polymer 1 100 100 100 100 Specificgravity 0.974 0.974 0.976 0.975 MFR (g/10 min, 190° C.) 4.2 4.0 3.3 3.2Hardness (Shore D) 58 59 59 59 UTS (ultimate tensile strength) (MPa)26.8 28.8 23.6 23.4 UTE (ultimate tensile elongation) (%) 392 405 373371 Golf ball weight (g) 45.25 45.22 45.32 45.30 Deflection (mm) 2.882.89 2.89 2.88 Initial velocity (m/sec) 76.71 76.69 76.66 76.67 AverageCOR (1^(st) shot to 10^(th) shot) 0.7721 0.7716 0.7720 0.7721 Shotnumber (durability) 175 179 196 194 Scuff resistance 3 3 3 3 Abrasionresistance good good good good Golf ball surface after trimming smoothsmooth smooth smooth with #1000, 4.5 sec Note: Numbers shown foringredients a to 1 in the table indicate parts by weight.

TABLE 2 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Na TPU-Mg TPU-Mg TPU-Mg Ionomer 1 Ionomer1 Ionomer 2 Ionomer 3 b. NaMB 7.40 — — — c. MgMB — 2.91 2.91 2.58 d. TPU— 20.0 20.0 20.0 e. a-1 — — 0.7 0.7 f. PO — — 0.23 0.2 g. Polymer 1 —59.2 59.2 56.8 h. Polymer 2 — 10.0 10.0 10.0 i. Polymer 3 — 10.8 10.8 —j. Polymer 4 — — — 13.2 k. TiO₂ 2.0 1.0 1.0 1.0 l. Blue pigment 0.030.03 0.02 0.02 g′. Polymer 1 100 — — — Specific gravity 0.961 0.9880.982 0.982 MFR (g/10 min, 190° C.) 2.6 5.1 2.3 2.3 Hardness (Shore D)62 57 58 54 UTS (ultimate tensile strength) (MPa) 30.6 23.1 25.5 17.6UTE (ultimate tensile elongation) (%) 387 359 388 317 Golf ball weight(g) 45.23 45.40 43.7 43.6 Deflection (mm) 2.81 2.97 2.72 2.73 Initialvelocity (m/sec) 76.82 76.46 76.60 76.55 Average COR (1^(st) shot to10^(th) shot) 0.7746 0.7664 0.7760 0.7754 Shot number (durability) 12252 164 167 Scuff resistance 3 3 3 3 to 4 Abrasion resistance poor goodgood good Golf ball surface after trimming smooth rough smooth lessrough with #1000, 4.5 sec

TABLE 3 Comparative Comparative Comparative Example 5 Example 6 Example7 TPU- TPU- TPU- NaMg NaMg NaMg Blend 1 Blend 2 Blend 3 Na Ionomer 1 5050 50 TPU-Mg Ionomer 1 50 TPU-Mg Ionomer 2 50 TPU-Mg Ionomer 3 50 MFR(g/10 min, 190° C.) 3.9 3.6 2.3 Hardness (Shore D) 60 60 58 UTS(ultimate tensile strength) (Mpa) 26.9 28.6 22.1 UTE (ultimate tensileelongation) (%) 381 406 364 Deflection (mm) 2.89 2.88 2.91 Initialvelocity (m/sec) 76.68 76.67 76.66 Average COR (1^(st) shot to the10^(th) shot) 0.7711 0.7706 0.7702 Shot number (durability) 171 181 183Scuff resistance 3 3 3 Abrasion resistance good good good Golf ballsurface after trimming smooth smooth smooth with #1000, 4.5 sec Note:The number “50” shown in the table for each ionomer indicates parts byweight.

Ingredient names in above Tables 1 and 2 are explained below.

a. Na.MgMB

-   -   Magnesium hydroxide/sodium carbonate/ethylene-methacrylic        acid-isobutyl acrylate terpolymer=13.0/37.0/50 wt %.        b. NaMB    -   Sodium carbonate/ethylene-methacrylic acid-isobutyl acrylate        terpolymer=50/50 wt %.        c. MgMB    -   Magnesium hydroxide/ethylene-methacrylic acid-isobutyl acrylate        terpolymer=50/50 wt %.        d. TPU    -   Aliphatic polyurethane (HMDI-PCL), produced by DIC-Bayer.        e. α-1    -   5-Norbornene-2,3-dicarboxylic anhydride, produced by Hitachi        Chemical Co., Ltd.        f. PO    -   2,5-Dimethyl-2,5-di(t-butylperoxy)hexyne-3, produced by NOF        Corporation.        g. Polymer 1    -   Ethylene-methacrylic acid copolymer (MFR, 60 g/10 min), produced        by DuPont.        g′. Polymer 1    -   Same as g. Polymer 1 appears twice in the tables for convenience        in contrasting the examples according to the invention with the        comparative examples.        h. Polymer 2    -   Ethylene-methacrylic acid copolymer (MFR, 500 g/10 min),        produced by DuPont.        i. Polymer 3    -   Ethylene-methacrylic acid-isobutyl acrylate (MFR, 31 g/10 min),        produced by DuPont.        j. Polymer 4    -   Ethylene-ethyl acrylate-maleic anhydride terpolymer (MFR, 7 g/10        min), produced by ARKEMA.        k. TiO₂    -   Tipaque PF737, produced by Ishihara Sangyo Kaisha.        l. Blue Pigment    -   Pigment Blue 29, produced by Toyo Ink.

The tests appearing in the tables are explained below.

MFR (g/10 min)

The melt flow rate was measured in accordance with JIS-K7210 at a testtemperature of 190° C. and a test load of 21.18 N (2.16 kgf).

Shore D Hardness

The Shore D hardness was measured in accordance with ASTM D-2240.

Tensile Elongation (%), Tensile Strength (MPa)

The tensile elongation and the tensile strength were measured inaccordance with JIS-K7161.

Deflection (mm)

The golf ball was placed on a steel plate, and the deflection (mm) bythe ball when compressed under a final load of 1,275 N (130 kgf) from aninitial load of 98 N (10 kgf) was measured. This test was carried out at23±1° C.

Initial Velocity (m/sec)

The initial velocity was measured using an initial velocity measuringapparatus of the same type as the USGA drum rotation-type initialvelocity instrument approved by the R&A. The ball was held for at least3 hours at 23±1° C., then tested at the same temperature by being hitwith a 250-pound (113.4 kg) head (striking mass) at an impact velocityof 143.8 ft/s (43.83 m/s). Ten balls were each hit twice. The time takento traverse a distance of 6.28 ft (1.91 m) was measured and used tocompute the initial velocity of the ball. This cycle was carried outover a period of about 15 minutes.

Coefficient of Restitution (COR)

The ball was fired from an air cannon against a steel plate at avelocity of 43 m/s, and the rebound velocity was measured. Thecoefficient of restitution (COR) is the ratio of the rebound velocity tothe initial velocity of the ball. Each value shown in the table is theaverage of ten measurements.

Shot Number (Durability)

The durability of the golf ball was evaluated using an ADC Ball CORDurability Tester produced by Automated Design Corporation (U.S.A). Aball was fired using air pressure and made to repeatedly strike twosteel plates arranged in parallel. The average number of shots requiredfor the ball to crack was treated as its durability. These averagevalues were obtained by setting four balls of the same type for thetesting, repeatedly firing each ball until it cracked, and averaging thenumber of shots required for each of the balls to crack. The type oftester used was a horizontal COR durability tester, and the incidentvelocity of the balls on the steel plates was 43 m/s.

Scuff Resistance

The golf balls were held at a temperature of 23±1° C. and hit at a headspeed of 33 m/s using a pitching wedge mounted on a swing robot machine,after which damage taken place by the impact was visually ratedaccording to the following scale.

Best: 1 point Better: 2 points Good (ordinary): 3 points Poor: 4 pointsPoorer: 5 points Poorest: 6 pointsAbrasion Resistance

A tubular container having a five-liter volume was filled with 15 golfballs and 1.7 liters of sand, after which the contents were mixed at 50rpm for 2 hours. The balls were then removed and, based on a visualdetermination of the extent of surface abrasion and decreased gloss dueto abrasion, the abrasion resistance was rated as follows.

Best

Better

Good (ordinary)

Poor

Poorer

Poorest

Ball Appearance after Surface Trimming

The surface of the injection-molded golf ball was trimmed with a #1000grinding wheel for 4.5 seconds, following which the surface appearanceof the ball was rated as follows.

Smooth

Less rough

Rough

The invention claimed is:
 1. A method for preparing a golf ball materialcomprising the following components (A), (B), and (C): (A) a mixture ofdifferent masterbatches prepared by separately masterbatching two ormore different metal ions (A1) or a masterbatch prepared bysimultaneously masterbatching two or more different metal ions (A2), (B)one or more polymer selected from the group consisting of dienepolymers, thermoplastic polymers and thermoset polymers, and (C) one ormore polymer having an acid content of from about 0.5 to about 30 wt %and selected from the group consisting of olefin-unsaturated carboxylicacid copolymers, olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester terpolymers, unsaturated carboxylicanhydride-containing polymers, unsaturated dicarboxylic acid-containingpolymers and unsaturated dicarboxylic acid half ester-containingpolymers, and further comprising, in admixture with components A, B andC, a norbornene dicarboxylic anhydride and/or a derivative thereof and aperoxide, the method being comprised of melt-mixing components B, C, thenorbornene dicarboxylic anhydride and/or a derivative thereof and theperoxide to form a polymer composition, then mixing component A into thepolymer composition so as to carry out in a single-step reaction(one-pass extrusion) which neutralizes the acid groups in theacid-containing polymer.
 2. The golf ball material-preparing method ofclaim 1, wherein the acid-neutralizing reactions of the acid groups inthe acid-containing polymer composition of components B, C, thenorbornene dicarboxylic anhydride and/or a derivative thereof and theperoxide with component A is carried out in a single-step with atwin-screw reaction extruder having arranged therein a screw segmenthaving a kneading disc zone.
 3. The golf ball material-preparing methodof claim 2, wherein the twin-screw reaction extruder has alength-to-diameter (L/D) ratio of at least
 20. 4. The golf ballmaterial-preparing method of claim 2, wherein the screw segment in thetwin-screw reaction extruder is arranged to have the kneading disc zonewith an L/D ratio ranging from about 10 to about 90% of the overall L/Dratio.
 5. The golf ball material-preparing method of claim 2, whereinthe twin-screw reaction extruder has a screw diameter of at least 15 mm.6. The golf ball material-preparing method of claim 2, wherein thetwin-screw reaction extruder has a vent port and a vacuum line connectedthereto.
 7. The golf ball material-preparing method of claim 2, whereinthe twin-screw reaction extruder is equipped with a device for thedropwise addition or pressurized injection of a liquid.
 8. The golf ballmaterial-preparing method of claim 7, wherein the liquid is a compoundshown by the formula ROH (R being hydrogen or an alkyl group) and isadded in an amount, based on the resin extrusion rate (the resinoutput), of 0.1 to 10 wt %.